Neonatal sepsis afflicts greater than 4 million infants a year with mortality as high as 40% in some series. Defects in adaptive and innate immunity have been cited as the primary reason as to why these patients are so incredibly vulnerable to septic insult. Though there are numerous studies describing the pathophysiology of sepsis in adults, there is substantially less in the neonatal literature. Therefore there is a significant need to further elucidate the immunological response of neonates to infection and sepsis. Toll like receptors (TLRs) are critical to the innate immune surveillance of pathogens and utilize the adaptor proteins MyD88 or TRIF to carry out downstream signaling events. Several published studies have demonstrated that neonatal peripheral blood mononuclear cells (PBMCs) have diminished responses to TLR ligands, including decreased MyD88 protein expression and cytokine production, compared to adults. Preliminary data presented in this application demonstrates that TRIF-/- neonates are more susceptible to cecal slurry (CS) induced sepsis than WT neonates. Further experimental evidence described in this proposal suggests that the production of the interferon inducible chemokine IP-10, is critical for the survival of neonates to sepsis. Therefore as IP-10 is the downstream consequence of TLR4 and TRIF signaling, the fundamental hypothesis of this proposal is that TLR4 and specifically TRIF signaling leading to the production of IP-10 is critical for the survival of neonates to CS induced sepsis. First, the contribution of TRIF signaling and downstream intracellular signaling events to the recruitment and/or activation of innate immune effector cells to the site of infection will be determined. Next, the significance of TLR4 agonist induced IP-10 production in the recruitment and/or activation of innate immunity will be elucidated. In sum, these experiments will not only define the role of TRIF and IP-10 in the survival of neonates to sepsis but will also provide targets for possible clinical intervention. PUBLIC HEALTH RELEVANCE: These studies will further the understanding of how the immune system of infants respond to severe infection. In addition, this project will identify potential targets for the development of therapeutics that can be used to prevent neonatal sepsis and improve patient outcomes.